A Kinetic Model for the Modification of Al2O3 Inclusions during Calcium Treatment in High-Carbon Hard Wire Steel

Laboratory-scale experiments for the modification of Al2O3 inclusions by calcium treatment in high-carbon hard wire steel were performed and the compositions and morphological evolution of inclusions were studied. The kinetics of the modification of Al2O3 inclusions by calcium treatment were studied in high-carbon hard wire steel based on the unreacted shrinking core model, considering the transfer of Ca and Al through the boundary layer and within the product layer, coupled with thermodynamic equilibrium at the interfaces. The diffusion of Al in the inclusion layer was the limiting link in the inclusion modification process. The Ca concentration in molten steel had the greatest influence on the inclusion modification time. The modification time for inclusions tended to be longer in the transformation of higher CaO-containing calcium aluminate. The modification of Al2O3 into CA6 was fastest, while the most time was needed to modify CA into C12A7. It took about six times time longer at the later stage of inclusion modification than at the early stage. The complete modification time for inclusions increased with the square of their radii. The changes of CaO contents with melting time were estimated based on a kinetic model and was consistent with experimental results.

Effects of Ti and Cu Addition on Inclusion Modification and Corrosion Behavior in Simulated Coarse-Grained Heat-Affected Zone of Low-Alloy Steels

In this paper, the effects of Ti and Cu addition on inclusion modification and corrosion behavior in the simulated coarse-grained heat-affected zone (CGHAZ) of low-alloy steels were investigated by using in-situ scanning vibration electrode technique (SVET), scanning electron microscope/energy-dispersive X-ray spectroscopy (SEM/EDS), and electrochemical workstation. The results demonstrated that the complex inclusions formed in Cu-bearing steel were (Ti, Al, Mn)-Ox-MnS, which was similar to that in base steel. Hence, localized corrosion was initiated by the dissolution of MnS. However, the main inclusions in Ti-bearing steels were modified into TiN-Al2O3/TiN, and the localized corrosion was initiated by the dissolution of high deformation region at inclusion/matrix interface. With increased interface density of inclusions in steels, the corrosion rate increased in the following order: Base steel ≈ Cu-bearing steel < Ti-bearing steel. Owing to the existence of Cu-enriched rust layer, the Cu-bearing steel shows a similar corrosion resistance with base steel.

Vapor-bubble growth in olivine-hosted melt inclusions

Melt inclusions record the depth of magmatic processes, magma degassing paths, and volatile budgets of magmas. Extracting this information is a major challenge. It requires determining melt volatile contents at the time of entrapment when working with melt inclusions that have suffered post-entrapment modifications. Several processes decrease internal melt inclusion pressure, resulting in nucleation and growth of a vapor bubble and, time permitting, diffusion of volatiles (especially CO2) into the vapor bubble. Previous studies have shown how this process may lead to most of the CO2 in the bulk melt inclusion being lost to the bubble. Without reconstruction, most of the melt inclusion data in the literature vastly underestimate the CO2 concentrations of magmas by measuring the glass phase only. Methods exist that attempt to reconstruct the entrapped CO2 contents, but they can be difficult to apply and do not always yield consistent results. Here, we explore bubble growth, evaluate CO2 reconstruction approaches, and develop improved experimental and computational approaches. Piston-cylinder experiments were conducted on olivine-hosted melt inclusions from Seguam (Alaska, U.S.A.) and Fuego (Guatemala) volcanoes at the following conditions: 500–800 MPa, 1140–1200 °C for Seguam and 1110–1140 °C for Fuego, 4–8 wt% H2O in the KBr brine filling the experimental capsules, and run durations of 10–120 min. Heated melt inclusions form well-defined S-CO2 trends consistent with degassing models. CO2 contents are enriched by a factor of ~2.5, on average, relative to those of the glasses in unheated melt inclusions, whereas S contents of heated and unheated melt inclusion glasses overlap, indicating that insignificant amounts of S partition into the vapor bubble. For naturally quenched melt inclusions, relatively low closure temperatures for CO2 diffusion enables some CO2 to enter vapor bubbles during quench, whereas higher closure temperatures for S diffusion limits its loss to vapor bubbles. We evaluate the timescales of post-entrapment processes and use the results to develop a new computational model to restore entrapped CO2 contents: melt inclusion modification corrections (MIMiC). Heated melt inclusion data are used as a benchmark to evaluate the results from MIMiC and other published methods of CO2 reconstruction. The methods perform variably well. Key advantages to our experimental technique are accurate measurements of CO2 contents and efficient rehomogenization of large quantities of melt inclusions. Our new computational model produces more accurate results than other computational methods, has similar accuracy to the Raman method of CO2 reconstruction in cases where Raman can be applied (i.e., no C-bearing phases in the bubble), and can be applied to the vast body of published melt inclusion data. To obtain the most robust data on bubble-bearing melt inclusions, we recommend taking both experimental- and MIMiC-based approaches.

Effect of Zr Additions on Non-Metallic Inclusions in X11CrNiMo12 Steel

The production of clean steel is associated with high-quality steel grades for demanding applications. The formation of oxide inclusions mainly depends on the deoxidation practice; it is usually carried out through Al additions, but alumina inclusions can have detrimental effects. An alternative zirconium inclusion modification was used in a creep-resistant steel to improve the cleanliness of laboratory-made steel. The thermodynamics behind the inclusion modification are presented, the reaction products are identified and the steel cleanliness improvement is quantified. The resulting influence of zirconium addition on non-metallic inclusions and mechanical properties is discussed. While the Zr additions drastically reduce the non-metallic inclusion size and area, additions above a certain amount result in the formation of zirconium nitrides that ultimately soften the martensitic steel due to the depletion of nitrogen in solid solution.

Inclusion Modification in C104Cr Saw Wire Steel with Different Cerium Content

In the present study, the effect of cerium content in the range of 0~0.0676% on oxygen and sulfur content, as well as the quantity, size, distribution, and type of inclusions in C104Cr saw wire steel, were investigated using thermodynamic analysis, metallographic examination, SEM-EDS, and component analysis. The results showed that conducting a vacuum carbon pre-deoxidization process is helpful in preventing the formation of Ce2O3 inclusions in a smelting experiment, and cerium has a beneficial effect in terms of modifying inclusions. When the content of cerium in steel is 0.0136% or 0.0277%, the main inclusions in the steel are Ce2O2S and CeS, and when the content of cerium is 0.0389% or above, the inclusions in the steel are Ce2O2S, CeS, Ce–S–O–P(As), Ce–O–P, and Ce–P(As). The calculation of the segregation model showed that the precipitation of CeP and CeAs in steel takes place at the end of solidification. According to the element mapping distribution diagram of Ce–S–O–P(As) and the layered Ce–O–P inclusions found in steel with high cerium content, two possible mechanisms for the formation of Ce2O3 inclusions distributed in the outer layer of cerium composite inclusions are proposed. The first mechanism suggests that Ce2O3 inclusions are generated from the combination of [Ce] and [O] directly, and the second suggests that Ce2O3 is the product of an oxidization reaction after the formation of CeP.

Effect of SiO2 containing slag for electroslag remelting on inclusion modification of 42CrMo steel

Five heats were carried out to study the effects of SiO2 containing slag for electroslag remelting (ESR) on inclusion characteristics of 42CrMo steel. Fluoride vaporization at elevated temperature from slags was also explored by thermogravimetric analysis. The results show that fluoride vaporization is dominated by slag viscosity and component activities in the melt. Slag composition has an important effect on the composition of the oxide inclusion. For 70 wt% CaF2–30 wt% Al2O3 slag, the compositions of oxide inclusions in remelted steel show no obvious differences compared with the virgin steel. Whereas, SiO2 content in oxide inclusions of steel processed by slag bearing SiO2 show an increasing trend with increase of SiO2 content in 50 wt% CaF2–CaO–SiO2 slag, and the MgO · Al2O3 inclusions are modified to (Al,Ca,Mg,Si)O inclusions with low melting temperature. Al2O3 contents in oxide inclusions are also closely related to the Al2O3 concentration in the molten slag, which increase with the addition of Al2O3 in slag bearing SiO2. In testing various slags, the incorporation of slag T2 with 50 wt% CaF2–30 wt% CaO–20 wt% SiO2 shows the highest cleanliness in remelted steel. This implies that slag T2 can be a promising slag for ESR process of alloy steel requiring Al content refinement due to less fluoride vaporization from slag and better inclusions modification.